Hoi,
I just reailised that with ultimate wiktionary, there will be a need to have an URL where the Ultimate Wiktionary will be located. I do not think it is acceptable to host the Ultimate Wiktionary as wiktionary.org as this is the current portal page. Therefore I think something like *ultimate.wiktionary.org* would be as good a choise as any.
When a Wiktionary decides to merge into the Ultimate wiktionary, this domain will be a redirect to the Ultimate Wiktionary. Technically there will be a need to redirect references in Wikipedia when a Wiktionary is migrated. Linking from the Ultimate Wiktionary to Wikipedia or any other project should remain the same. It should be obvious that the Ultimate Wiktionary can use all resources of all Wiktionaries. It is as obvious that any Wiktionary can use the resources of the Ultimate Wiktionary.
Thanks, GerardM